Re: [PATCH v3 4/8] eal: fix hotplug add / remove

[Jan Blunck <jblunck@infradead.org>]

On Tue, Jul 11, 2017 at 7:25 PM, Gaetan Rivet <gaetan.rivet@6wind.com> wrote:
> The hotplug API requires a few properties that were not previously
> explicitly enforced:
>
>   - Idempotency, two consecutive scans should result in the same state.
>   - Upon returning, internal devices are now allocated and available
>     through the new `find_device` operator, meaning that they should be
>     identifiable.
>
> The current rte_eal_hotplug_add implementation identifies devices by
> their names, as it is readily available and easy to define.
>
> The device name must be passed to the internal rte_device handle in
> order to be available during scan, when it is then assigned to the
> device. The current way of passing down this information from the device
> declaration is through the global rte_devargs list.

This only true for the virtual bus (vdev).

>
> Furthermore, the rte_device cannot take a bus-specific generated name,
> as it is then not identifiable by the `find_device` operator. The device
> must take the user-defined name. Ideally, an rte_device name should not
> change during its existence.
>
> This commit generates a new rte_devargs associated with the plugged
> device and inserts it in the global rte_devargs list. It consequently
> releases it upon device removal.

So unplugging a device which devargs have been passed via the command
line is implicitly removing the command line parameter? This is a
surprising side-effect and it sound wrong to do. What happens if the
device is getting replugged?

It seems to me that you want to make the hotplug add functionality
behave like a force attach. You can achieve this by calling
rte_eal_devargs_add/parse before calling into hotplug add.


> Fixes: a3ee360f4440 ("eal: add hotplug add/remove device")
>
> Signed-off-by: Gaetan Rivet <gaetan.rivet@6wind.com>
> ---
>  lib/librte_eal/common/eal_common_dev.c | 57 ++++++++++++++++++++++++++++++++--
>  1 file changed, 54 insertions(+), 3 deletions(-)
>
> diff --git a/lib/librte_eal/common/eal_common_dev.c b/lib/librte_eal/common/eal_common_dev.c
> index 32e12b5..f5566a6 100644
> --- a/lib/librte_eal/common/eal_common_dev.c
> +++ b/lib/librte_eal/common/eal_common_dev.c
> @@ -118,11 +118,32 @@ int rte_eal_dev_detach(struct rte_device *dev)
>         return ret;
>  }
>
> +static char *
> +full_dev_name(const char *bus, const char *dev, const char *args)
> +{
> +       char *name;
> +       size_t len;
> +
> +       len = strlen(bus) + 1 +
> +             strlen(dev) + 1 +
> +             strlen(args) + 1;
> +       name = calloc(1, len);
> +       if (name == NULL) {
> +               RTE_LOG(ERR, EAL, "Could not allocate full device name\n");
> +               return NULL;
> +       }
> +       snprintf(name, len, "%s:%s,%s", bus, dev,
> +                args ? args : "");
> +       return name;
> +}
> +
>  int rte_eal_hotplug_add(const char *busname, const char *devname,
>                         const char *devargs)
>  {
>         struct rte_bus *bus;
>         struct rte_device *dev;
> +       struct rte_devargs *da;
> +       char *name;
>         int ret;
>
>         bus = rte_bus_find_by_name(busname);
> @@ -137,21 +158,49 @@ int rte_eal_hotplug_add(const char *busname, const char *devname,
>                 return -ENOTSUP;
>         }
>
> +       name = full_dev_name(busname, devname, devargs);
> +       if (name == NULL)
> +               return -ENOMEM;
> +
> +       da = calloc(1, sizeof(*da));
> +       if (da == NULL) {
> +               ret = -ENOMEM;
> +               goto err_name;
> +       }
> +
> +       ret = rte_eal_devargs_parse(name, da);
> +       if (ret)
> +               goto err_devarg;
> +
> +       ret = rte_eal_devargs_insert(da);
> +       if (ret)
> +               goto err_devarg;
> +
>         ret = bus->scan();
>         if (ret)
> -               return ret;
> +               goto err_devarg;
>
>         dev = bus->find_device(NULL, cmp_detached_dev_name, devname);
>         if (dev == NULL) {
>                 RTE_LOG(ERR, EAL, "Cannot find unplugged device (%s)\n",
>                         devname);
> -               return -EINVAL;
> +               ret = -ENODEV;
> +               goto err_devarg;
>         }
>
>         ret = bus->plug(dev, devargs);
> -       if (ret)
> +       if (ret) {
>                 RTE_LOG(ERR, EAL, "Driver cannot attach the device (%s)\n",
>                         dev->name);
> +               goto err_devarg;
> +       }
> +       free(name);
> +       return 0;
> +
> +err_devarg:
> +       rte_eal_devargs_remove(busname, devname);
> +err_name:
> +       free(name);
>         return ret;
>  }
>
> @@ -179,6 +228,8 @@ int rte_eal_hotplug_remove(const char *busname, const char *devname)
>                 return -EINVAL;
>         }
>
> +       rte_eal_devargs_remove(busname, devname);
> +       dev->devargs = NULL;
>         ret = bus->unplug(dev);
>         if (ret)
>                 RTE_LOG(ERR, EAL, "Driver cannot detach the device (%s)\n",
> --
> 2.1.4
>